Many hydrocarbonaceous mineral streams contain some small proportion of diamondoid compounds. These high boiling, saturated, three-dimensional polycyclic organics are illustrated by adamantane, diamantane, triamantane and various side chain substituted homologues, particularly the methyl derivatives. These compounds have high melting points and high vapor pressures for their molecular weights and have recently been found to cause problems during production and refining of hydrocarbonaceous minerals, particularly natural gas, by condensing out and solidifying, thereby clogging pipes and other pieces of equipment. For a survey of the chemistry of diamondoid compounds, see Fort, Jr., Raymond C., The Chemistry of Diamond Molecules, Marcel Dekker, 1976.
In recent times, new sources of hydrocarbon minerals have been brought into production which, for some unknown reason, have substantially larger concentrations of diamondoid compounds. Whereas in the past, the amount of diamondoid compounds has been too small to cause operational problems such as production cooler plugging, now these compounds represent both a larger problem and a larger opportunity. The presence of diamondoid compounds in natural gas has been found to cause plugging in the process equipment requiring costly maintenance downtime to remove. On the other hand, these very compounds which can deleteriously affect the profitability of natural gas production are themselves valuable products.
The problem of diamondoid deposition and plugging in natural gas production equipment has been successfully addressed by a controlled solvent injection process. U.S. Pat. No. 4,952,748 to Alexander and Knight teaches the process for extracting diamondoid compounds from a hydrocarbon gas stream by contacting the diamondoid-laden hydrocarbon gas with a suitable solvent to preferentially dissolve the diamondoid compounds into the solvent. Allowed U.S. Pat. application Ser. No. 489,111, filed Mar. 6, 1990, to Cullick and Roach teaches a method for locating the solvent injection point within the natural gas wellbore.
Further studies have revealed that separation of the diamondoid compounds from the diamondoid-enriched solvent is complicated by the fact that numerous diamondoid compounds boil in a narrow range of temperatures surrounding the boiling range of the most preferred solvents U.S Pat. Nos. 4,952,747, 4,952,749, and 4,982,049 to Alexander et al. teach various methods of concentrating diamondoid compounds in the solvent for, among other reasons, recycling the lean solvent fraction for reuse, and each of these processes produces an enriched solvent stream containing a mixture of diamondoid compounds. While these techniques meet the industrial need for a constant supply of relatively lean solvent for continuous recycle, the diamondoid-enriched streams rejected by these processes are not sufficiently pure to themselves be commercially useful. As mentioned above, conventional distillation of diamondoid-containing solvent mixtures is complicated by the fact that diamondoid compounds exhibit vapor pressures which are unusually high for their molecular weights. Further, the relative volatilities of recovered diamondoid mixtures and commonly used solvents such as diesel fuel tend to converge at elevated temperatures, impeding effective partitioning of solvent and diamondoid compounds. Thus it can clearly be seen that a method for recovering diamondoid compounds in relatively high purity from a diamondoid-containing solvent would be highly desirable.